Shothole drilling method



March 25, 1969 R. E. LOWE SHOTHOLE DRILLING METHOD Sheet 0f2 Filed July 29, 1966 FIG. I

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lNVENTOR VI E N m E T T w A L S E H R March 25, 1969 R. E. LOWE SHOTHOLE DRILLING METHOD Sheet Filed July 29, 1966 Fl G. 4

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INVENTQRZ R. E. LOWE H I: ATTORNE United States Patent 3,434,549 SHOTHOLE DRILLING METHOD Raymond E. Lowe, Livingston, Tex., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed July 29, 1966, Ser. No. 568,938 Int. Cl. EZlb 47/00, 7/00 US. Cl. 175-1 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method for drilling seismic exploration shotholes. More specifically, this invention relates to a method for drilling a seismic exploration shothole which permits an explosive charge to be placed at the bottom of the hole before the bit and drill string are removed therefrom.

In conventional shothole drilling, a :borehole is drilled through the surface strata of the earth. Into this boreholeis placed a charge of dynamite or other explosive. When the explosive is detonated, shock waves emanate from the explosion and pass through the various strata of the earth formation. These shock waves are received as signals by a seismometer and placed at a location distant from the point of the explosive, which records the quality of such incoming shock waves. The summation of such recorded data from a number of explosive events is processed to reveal the nature of the earth-foaming strata within the proximity of the explosions.

In order to survey accurately a large area, it is necessary to provide a large number of seismic shots (explosions) geometrically distributed over the area in a gridlike pattern. Furthermore, each of these explosions should take place at a subsurface depth of from several to several hundred feet. In order to place the explosive charge that is necessary to cause the seismic event at the required depth, it is necessary to drill a hole in the earth for each event location. Such holes are known in the art as shotholes.

When shotholes are drilled in areas where the bore remains open and competent because of the hardness of the formation, the explosive charge may be placed in the open hole, after the drill string is removed, by tamping rods. However, in areas of soft earth, marshy locations or where the location is covered with water, the hole will not remain open and easing must be set in order to line the bore of the hole so the explosive charge may be placed in the bottom thereof. In recreation lakes and most other water locations it is necessary to remove this casing after the charge has been exploded to avoid :being hazardous to boating and other water activities. It is very diflicult and expensive to clean out all of the casing from such locations because the explosion often bends or damages the casing which is of the thin wall type.

Since shotholes are usually drilled with an open bore drill string, it has been proposed to construct the drill bit of cast iron so the bit may be fractured and knocked from the drill string when the desired depth has been reached. By removing the bit from the end of the drill string while both are in the hole allows the explosive charge to be lowered through the drill string open bore to the hole bottom and obviates the necessity for casings. Obviously, however, a new ibit must be used for each location.

Summary of the invention It is therefore an object of this invention to provide a method for rapidly and efficiently drilling and explosively charging seismic shotholes.

It is another object of this invention to provide a method of explosively charging a shothole by lowering the explosive through an open bore in the drill string and bit.

These and other objects have been attained in the present invention by providing a method of drilling and explosively charging a seismic shothole wherein a shothole is drilled in the earth by means of a non-coring drill bit and drill string. The bit has a central bore in communication with the interior of the drill string so that drilling fluid may be continuously circulated therethrough during the drilling operation. This bore is interrupted by a crossbar which, by means of a tarnping' rod, weight or other means, may be knocked out of the way when the shothole reaches total depth. With the crossbar removed from its obstructive position across the bit bore, an explosive charge may be lowered down the bore of the drill string and through the bit to the bottom of the hole when the bit has been raised from the bottom of the hole. The bit, crossbar and drill string are then removed from the shothole and prepared for drilling at another location by merely repositioning the crossbar across the bit bore.

These and other objects will become evident from the following description of the drawings wherein:

FIGURE 1 is a perspective view of the cutting end of the drill bit used with the instant invention;

FIGURE 2 is an orthographic end view showing the cutting end of the bit illustrated by FIGURE 1;

FIGURE 3 is a diagrammatic view taken in partial cross-section of a seismic shothole showing a portable rotary drilling rig therefor; and

FIGURES 4-6 are views taken in partial cross-sections of a seismic shothole showing several stages of preparation and explosive charging according to this invention.

The drill bit 10, shown by FIGURES 1 and 2, includes a main tubular body portion having a threaded tubular shank 11 at one end thereof. The bit and threaded shank has a wide opening through bore 13 extending centrally therethrough. At the cutting end of the bit body, cutting portions or teeth 12 formed in a saw-tooth shape are formed from the wall of the bit body around the circumference thereof. Adjacent to the cutting teeth 12 and flush with the vertical face thereof is provided rib portions or protrusions 12a. These rib portions 12a extend along the length of the bit body and provide supporting structure for a powdered metal, tungsten carbide, for example, cutting tip insert 22.

Across the respective faces of two diametrically opposed ribs 12a and cutting portions 12 is provided a crossbar 14. The respective ribs are provided with holes 17 and 18. Opposite ends of the crossbar 14 are provided with holes 16 and 19 through one cooperative set of holes 18 and 19 is provided a pivot pin 21. The other set of holes 16 and 17 accommodate a shear pin 20.

Across the lower face of the crossbar 14 is provided oppositely directed pairs of teeth 15 having, for example, tungsten carbide cutting surface inserts 23.

In operation, the bit 10 is attached to the lower end of a drill string 33 as shown at FIGURE 3 that is suspended from a light derrick structure 31 and powered by a portable rig such as that shown at 32. The derrick and rotary power may be mounted on a truck, as shown,'or on a barge or a boat, any of which means is highly mobile to quickly remove the drilling rig from one location to the other.

The wide opening of the bit through-bore 13 will accommodate relatively large volumes of air, water or other drilling fluids at relatively low pressure drop across the bit. This is advantageous due to the consequent high chip removal capacity afforded by a small, low power fluid pump. A high chip removal rate is directly related to the drilling rate which also is relatively high.

Only the crossbar 14 obstructs the through-bore 13 which is necessary only to cut and fragment the inner core that is cut by the peripheral row of teeth 12. The effect of the crossbar is to crush and abrade the inner core, thereby breaking it up into fragments which are then swept away and up the well annulus formed between the wellbore wall and the outside diameter of the drill string to the surface.

When the shothole has been drilled to total depth, the bit is lifted oit the hole bottom a distance of at least one bit diameter. A tamping rod or weight 34 on a wire line 35 is then lowered through the drill string bore where it is dropped against the crossbar 14. The impact of the weight 34 against the crossbar 14 causes the pin 20 to shear, thereby releasing that side of the crossbar from the bit. When released, the crossbar 14 will swing down below the bit and away from its drilling position of obstructing the bore 13.

As shown in FIGURE 5, the weight 34 is removed from the hole and explosive charge 36 is attached to the wire line 35 and lowered through the bore of the drill string and the bit through-bore -13 to the hole bottom where it is disconnected from the wire line 35 and left in place.

As the explosive charge 36 is lowered through the drill string bore, electric detonating wires 37 trail back up the bore to the surface where they are firmly secured to a float 38. When the drill string and bit are removed from the hole the wires and float are allowed to strip their way through the bore and fall free from the bit when it clears the surface. From the surface, the float 38 is retrieved along with the detonation wires 37 where they may be attached to an electrical explosive detonator not shown.

FIGURE 6 shows the explosive charge 36 in place with detonation wires 37 connected to the charge and extending from the hole. If desired, the explosive charge may be covered with back-fill 39.

It may therefore be seen that by employing the principles of this invention a shothole may be drilled in any type of formation or surface condition without concern for setting and removing casing pipes or premature backfilling. Furthermore, the drilling rig is ready to be moved to another location as soon as the bit is retracted from the hole by merely securing the crossbar 14 back into drilling position with another shear pin 20.

I claim as my invention:

1. A method of explosively charging a seismic shothole drilled into the earth with a rotary non-coring bit having a removable center portion assuming an obstructing position across the vertical axis of a central fluid course through a drill string which carries said bit, said method comprising the steps of: v

4 drilling said'shothole in'the earth with-said drill string and said non-coring bit while circulating fluid through said drill string and non-coring bit to keep them open at all times;

lifting said non-coring bit at least one bit diameter above the bottom of said hole; removing said bit center portion from across the vertical axis of said fluid course to a non-obstructing position;

lowering an explosive charge through said drill string fluid course and said non-coring bit to said hole bottom; and

removing said drill string, said non-coring bit and said bit center portion from said shothole prior to detonating said explosive charge.

2. The method of claim 1 wherein said step of removing said bit center portion comprises the shearing of at least one pin securing said center portion of said non-coring bit.

3-. The method of claim 1 wherein said explosive charge has electrical ignition conduits secured thereto, said igni tion conduit having float means secured thereto at an end opposite from said explosive charge;

said step of removing said drill string, said non-coring bit and said bit center portion from said shothole comprising stripping said non-coring bit and drill string over said float and conduit; and

recovering said float and conduit from surface environs of said shothole for connection to electrical detonation means.

4. A method of installating an explosive charge below the surface of unconsolidated earth, said method comprising the steps of:

drilling with a non-coring bit a substantially vertical hole in said earth with the formation of earth cuttings along the bottom of the bit; circulating fluid into said hole while drilling to clear away the earth cuttings from the bit and to assist in providing a partially obstructed through passage in said hole free of earth cuttings with the obstruction lying along the vertical axis of the through passage;

removing the partial obstruction from the through passage after the drilling has stopped, thereby creating an open through passage;

lowering an explosive charge through said open through passage to the bottom of said hole;

simultaneously preventing earth from filling said hole prior to said explosive charge reaching bottom; and subsequently removing said open through passage, said bit and said obstruction fromsaid hole and positioning earth material above said explosive charge.

References Cited UNITED STATES PATENTS 2,793,833 5/1957 Daniel --1 2,880,967 4/1959 Blount 1751 2,883,154 4/1959 Daniel 175--1 2,890,861 6/1959 Cook 175-1 X 3,100,542 8/1963 Stark 175-67 X DAVID H. BROWN, Primary Examiner.

US. Cl. X.R. 17557 

